I can't get my head around this. Can anyone help?

Given two string arrays, I need to create a third array/string which contains the additions...

e.g.

ARRAY1
Bob
Jane
Paul

ARRAY2
Bob
Mary
Jane
Paul
John

I need a routine that will tell me that Mary and John have been added - e.g. a string result of "Mary,John"

Also, it's possible that some items originally in ARRAY1 might not be present in ARRAY2.

e.g.

ARRAY1
Bob
Jane
Paul

ARRAY2
Mary
Jane
John

Again, all I want to know is that Mary and John were added to the array - I don't need to know that Bob and Paul were removed.

Can anyone help?